A recent letter from the EPA to the Oregon Department of Environmental Quality raises questions that small amounts of chemical agent may be getting into the air at the Umatilla Chemical Depot.

The amount of agent noted by the stations is well below the amount used for civilian limits. For example, the exposure limit for sarin is O.000003 milligrams per cubic meter (mg/m3). The greatest amount of sarin noted in the early summer 2000 was 0.000000137 mg/m3 - 21 times less than the exposure limit.

The amount for the public, set by U.S. Surgeon General, is the allowable concentration for indefinite, unprotected lifetime exposure of the general population without adverse health effects.

The depot checks for readings at the chemical agent worker level, which is about 10 times higher the civilian levels. For sarin, the worker limit is 0.0001 mg/m3, but the depot checks at one quarter of that - 0.000025 mg/m3. One system, the perimeter monitoring network is calibrated to detect at even lower levels.

This is similar to taking a grain of salt, dividing it into 1,000 pieces and then trying to find one piece in a cubic meter of air, said depot spokeswoman Mary Binder.

The readings on the EPA's chart are well below that, and could be caused by anything from electricity to airborne herbicides, which have similar chemical structures to the chemical agents, Binder said.

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